The “energy gap” in portable electronics is making microstructured fuel cells an increasingly attractive technology. Microfluidic fuel cells, or laminar flow-based fuel cells, represent a new type of small scale fuel cell technology based on inexpensive microfabrication methods and low-cost materials. A microfluidic fuel cell is defined as a device that incorporates all fundamental components of a fuel cell to a single microfluidic channel and its walls. These fuel cells operate without a membrane, and the most common configurations rely on the laminar nature of microscale flows to maintain sufficient separation of fuel and oxidant streams. Ionic charge transfer is facilitated by a supporting electrolyte contained in the co-laminar streams. Inter-diffusion is restricted to an interfacial width at the center of the channel, and the electrodes are positioned sufficiently far away from this inter-diffusion zone to prevent crossover effects. Microfluidic fuel cells provide a number of unique advantages: fuel and oxidant streams may be combined in a single microchannel; no ion exchange membrane is needed; sealing, manifolding, and fluid delivery requirements are reduced; and issues related to membrane hydration and water management are eliminated.
Proof-of-concept microfluidic fuel cell devices have been demonstrated based on a number of fuels, including vanadium ions, formic acid, methanol, hydrogen, and hydrogen peroxide, combined with oxidants such as vanadium ions, oxygen, or hydrogen peroxide. The power densities of these cells were mainly restricted by the solubility of the reactants and the associated rate of convective/diffusive mass transport to the active sites. Cell designs using oxygen have the benefit of ‘free’ oxidant available in the ambient air. Air-breathing designs, however, require a blank cathodic electrolyte stream and have shown moderate power densities. The highest power density levels of the microfluidic fuel cells reported to date were achieved using vanadium redox couples in both half-cells; V2+/V3+ as anolyte and VO2+/VO2+ as catholyte. These vanadium redox fuel cells benefit from a rapid and balanced electrochemical system in terms of species transport characteristics and reaction rates, as well as a relatively high open-circuit voltage (˜1.5 V). In addition, the vanadium redox reactions take place on carbon electrodes without any electrocatalyst requirements. In the foregoing microfluidic fuel cell designs, the reactants, products and electrolyte are typically in the same liquid phase, and the reaction zones are simple solid-liquid interfaces. These characteristics provide potential for a variety of three-dimensional fuel cell architectures.
One such design is disclosed in U.S. Pat. No. 7,157,177. The electrode structure adapted for use with a fuel cell system (e.g., a hydrogen or a direct hydrocarbon fuel cell system), has an electrode structure comprising a substrate or support structure having one or more discrete porous bulk matrix regions disposed across a top surface of the substrate. Each of the one or more discrete porous bulk matrix regions is defined by a plurality of acicular pores that extend through the substrate or support structure. The plurality of acicular pores define inner pore surfaces, and the inner pore surfaces have a conformal electrically conductive layer thereon, as well as a plurality of catalyst particles.
The capability of reaching high levels of fuel utilization per single pass has been a major challenge associated with microfluidic fuel cell technology to date. It is an object of the present technology to overcome the deficiencies in the prior art.